Among electrophotographic photosensitive members, since those using an organic photoconductive material have good film formability and can be produced by coating, these have an advantage of being capable of providing electrophotographic photosensitive members having a high productivity and a low price.
Although electrophotographic photosensitive members are broadly classified into positively charging ones and negatively charging ones depending on polarities of charges when their surfaces are charged, in the case of electrophotographic photosensitive members using an organic photoconductive material, more thereof are negatively charging electrophotographic photosensitive members.
Although electrophotographic photosensitive members generally have a support and a photosensitive layer formed on the support, for a photosensitive layer of a negatively charging electrophotographic photosensitive member, a photosensitive layer containing a charge generation material and a hole transport material (hereinafter, also referred to simply as “photosensitive layer”) is used. The photosensitive layer containing a charge generation material and a hole transport material includes a photosensitive layer in which a charge generation layer containing a charge generation material and a hole transport layer containing a hole transport material are provided in this order from the support, and a photosensitive layer in which a charge generation material and a hole transport material are contained in the same layer.
If a photosensitive layer (charge generation layer) is provided directly on the support, exfoliation of the photosensitive layer (charge generation layer) is generated and defects (shape defects such as flaws or material defects such as impurities) on the surface of the support are reflected on images as they are, and image defects such as black spots and blank areas are generated in some cases.
In order to solve these problems, in many electrophotographic photosensitive members, a layer called an undercoat layer (also called an intermediate layer) is provided between the photosensitive layer and support.
However, deteriorations of characteristics of an electrophotographic photosensitive member, considered to be caused by the undercoat layer, are observed in some cases.
Then, attempts have conventionally been made to improve characteristics of the undercoat layer by making an electron transport material contained in the undercoat layer (Patent Literatures 1 and 2) to convert the undercoat layer to an electron transport layer.